The patent, entitled "Capacitive Sensor Packaging," almost exactly mirrors the implementation found in Apple's latest flagship handset. The packaging includes a "responsive element" that detects the proximity of a user's fingerprint— the stainless steel ring that surrounds the iPhone 5s home button— and a sensor cover made of "an anisotropic dielectric material, for example sapphire."

Touch ID's aesthetic treatments have been included as well, as the patent details "an ink assembly...printed on the lens" that "has the effect that the otherwise-translucent button can be made opaque, so the elements of the fingerprint recognition sensor are not immediately visible to the user."

Other methods of proximity detection— like optical or infrared sensing— are also covered. The filing predicts that new methods like these might be needed in the future because requiring a user to place their finger within a specific area limits "the design flexibility for the fingerprint recognition sensor."

An earlier Apple patent application showing a method for embedding a fingerprint sensor inside an LCD.

Interestingly, the patent leaves open the possibility of embedding the sensor behind a "display element." This marks the second mention this year of an in-display fingerprint sensor, after a separate patent filing surfaced in June detailing a method of embedding a fingerprint sensor within an LCD.